The invention relates to a drive device, in particular having a motor and a gear transmission.
The demand for highly dynamic drives is rising with the increasing electrification of the motor vehicle and also in general mechanical engineering. Examples are electric actuators for brakes, chassis suspensions, steering and robotics.
In line with the trend for electrifying all sectors of industry, more and more electric motors (EM) are being used as actuating drives. This particularly applies for electric motors (EM) having a spindle drive and a ball screw assembly. In automotive engineering, in particular in future brake systems, such as integrated systems and electromechanical braking (EMB) for a) drives of the brake linings and b) drives for pistons. In both cases, a suitable bearing support for the rotor and the spindle is required.
In DE 10 2005 040389 A1, a motor concept is described which has a considerably smaller rotating mass than other comparable motors by the magnets being attached to a thin-walled rotor and the magnetic back iron occurring via a second air gap via a fixed inner stator. However, due to bearing support on both sides with two inner stators the assembly is more complex in comparison to the conventional motor with rotating back iron and one air gap.
With many drives, the rotational movement is translated into a linear movement via a ball screw assembly with a nut and screw spindle. Here, the rotating mass of the nut forms part of the dynamics. In addition, with this drive it is necessary to support the torque and to provide a spring for resetting the screw spindle to the starting position.
In the case of the device according to DE 10 2010 045617 of the applicant, normally the ball screw assembly and the bearing are only stressed from one side by positive axial forces which essentially occur by means of the compressive force on the piston. However, relatively small radial forces of approximately 10% also act on the bearing support. The occurrence of a fault, however, when e.g. the piston push rod jams, has to be taken into consideration. Here, the pedal force acts on the piston push rod such that a negative axial force acts on the ball screw assembly and the bearing support. A further fault can occur when the rotor impinges on the sharp-edged stator tooth, which can result in the rotor becoming blocked and hence the drive. When all these faults occur, the effect of the secondary braking should be functional. These fault occurrences are very rare and are recognised by the diagnostics. The vehicle must then be taken for a service.
A typical use of an integrated four-point contact bearing for the ball screw assembly is also already known from DE 197 57 038, in which the rotor is supported on the ball screw assembly. The rotor and sensor drive are arranged on one side of the ball screw assembly.
DE 10 2008 059 862 and DE 10 2010 050 132 use two bearings for the rotor and the ball screw assembly, in which the rotor is arranged on one side of a bearing and the sensor drive is arranged on the other side.